Research On Quantum Communication And Quantum Gate Based On The Solid Optical Cavity Quantum Electrodynamics Systems

Quantum information science is the application of quantum mechanics in the field of information science. Secure quantum communication and reliable quantum computation are the two most important branches of quantum information science. My research introduced in this thesis involves the quantum entanglement purification and concentration, universal quantum logic gate, and quantum information processing in decoherence-free subspace based on the cavity quantum electrodynamics systems, and has a lot of novel results.First, we propose an efficient atomic entanglement purification scheme based on the coupled cavity-atom system and the coherent state cavity input-output process. Remote parties in quantum communication can construct the parity-check modules, and distill a high-fidelity atomic entanglement ensemble from an initial mixed state ensemble by using the parity-check measurments. The proposed process can further be used for unknow atomic states entanglement concentration, i.e., distilling the maximally entangled atomic states from the initial unmaximally entangled atomic ensemble. Also by using the parity-check measurement,we described a modified atomic entanglement concentration scheme,by introducing the ancillary single atoms. Compared with previous works also based on the cavity quantum electrodynamics, we use the coherent optical pulse rather than single photon to perform the quantum channel,meanwhile,the coherent state input-output process is robust and scalable by working in low-Q cavity in the atom-cavity intermediate coupling region. Furthermore, the detection in the parity check is based on the intensity of the outgoing coherent states, which is more efficient than single-photon detection and can be easily achieved with currently available technologies. Thus, our new proposed schemes have a higher experimental feasibility. Moreover, the model and method used in the schemes can also be used in other quantum information processing tasks,such as optimal entanglement concentration, scalable quantum computation, multipartite entanglement concentration, and so on.Second, we investigate and propose the schemes for entanglement concentration and quantum gate based on the nitrogen-vacancy center and microtoroidal resonator coupled systems. On the one hand, we propose an entanglement concentration scheme for partially entangled Bell state and GHZ state, and an enganglement concentration scheme for partially entangled W-class state on nitrogen-vacancy centers. These two schemes have the similar idea, and have a lot of advantages compared to previous entanglement concentration schemes. All these advantages greatly decrease the difficulty of the implementation of the schemes in experiments and make the schemes more feasible and useful in practical applications. On the other hand, we focus our attention on how to realize a nonlocal multi-qubit gate by using the nitrogen-vacancy center and microtoroidal resonator coupled systems, and propose a theoretical scheme to implement a nonlocal N-qubit conditional phase gate. The physical realization of the scheme can be greatly simplified, which can work nonlocally among spatially separated nodes in a quantum network for realizing quangum entanglement distribution and quantum information processing.Third, we propose the schemes for cluster state entanglement generation and concentration on nitrogen-vacancy centers in decoherence-free subspace, based on the nitrogen-vacancy centers and optical microcavity coupled systems. The coupled system used in the schemes is a potentially practical model by considering the currently available techniques, which is well suited for the systemic preparation of cluster states in one-way quantum computation. Accompanied with the optimal entanglement concentration protocol for the logic-qubit expanded cluster state, one can efficiently preserve the maximal entanglement.Compared with the previous studies of atomic systems, the composite system used in our scheme is helpful in stabilizing the coupling strength,and the logic-qubit entangling gate might be constructed with simpler configurations.